The invention is primarily applicable to materials such as bauxites, bauxitic clays, kaolinitic clays and mixtures thereof that have present as major impurities iron and titanium in various forms.
There has been a great deal of research and there is a vast quantity of literature in attempts to produce a relatively iron-free alumina, alumina-silica product and iron-free aluminum chloride from such raw materials. None of the processes proposed have been shown to be economically successful.
This problem can best be described by the following references: Landsberg Chlorination Kinetics of Aluminum Bearing Minerals: Metallurgical Transactions B, Volume 6B, June, 1985; pages 207-208. To quote from page 208, first column:
"Whereas Foley and Tittle showed that iron could be removed from pre-reduced bauxite by chlorination to produce a refractory grade alumina, FIG. 2 indicates that a substantial loss of alumina accompanies the initial rapid iron chlorination under reducing conditions. Even if this loss could be tolerated the remaining iron is too high for producing cell grade alumina or aluminum chloride." PA1 "In general, the reduction of aluminum-containing materials with chlorine in the presence of reducing carbon in some form to produce aluminum chloride is an old and generally well-known reaction and one of the suggested expedients referred to above utilized Bauxite as the alumina containing material. Bauxite however, normally contains many impurities including iron oxide, silica, and titania. Since these impurities readily react with chlorine in the presence of carbon to form iron, silicon, and titanium chlorides, the usual gaseous aluminum chloride reaction effluent therefrom must be subjected to cumbersome and expensive after-purification measures if these chloride contaminants are to be separated to provide even a reasonably pure aluminum product." PA1 "The raw materials that may be used for the preparation of AlCl.sub.3, include bauxite, clays, shale, anorthosite, coal ash, and many other aluminum containing materials. Bauxite or clays are the most logical choices because of their higher Al.sub.2 O.sub.3 contents and the large reserves of these materials available. Iron is the impurity most deleterious to the process since it uses up chlorine and is difficult to remove from the product." PA1 "It is true that when processing between 900.degree. C.-1150.degree. C. titanium is removed from the original material along with the iron in the form of titanium tetrachloride, but only in small amounts unless a large excess of aluminum chloride is used." PA1 "(b) Excess AlCl.sub.3 that is used is recovered at a low cost as an impure AlCl.sub.3 containing FeCl.sub.3 and returned to the Number One Chlorination stage without any deleterious effects on chlorinating the contained iron and titanium minerals." PA1 "First, the clay or bauxite undergoes a pelletizing step wherein a hydrochloric acid binder solution is added and it is pelletized into high-density, high strength pellets in conventional equipment such as an extrusion type pelletizer." PA1 "Attempts to remove iron from the pellets by chlorinating under reducing or neutral conditions are not feasible because of cochlorination of excessive amounts of alumina." PA1 (a) Removal of any free moisture as steam. PA1 (b) Breaking down of the bond of water of crystallization in aluminum oxide minerals wherein a high percentage of water of crystallization is driven off as steam. PA1 (c) Breaking down of the chemical bond or bonds of complex aluminum minerals such as Kaolinite, Al.sub.2 O.sub.3 .multidot.2SiO.sub.2 .multidot.2H.sub.2 O, wherein the H.sub.2 O is driven off as steam and Al.sub.2 O.sub.3 and SiO.sub.2 are converted into amorphous Al.sub.2 O.sub.3 and amorphous SiO.sub.2 respectively. To accomplish satisfactory calcination of bauxites and clays, a temperature range of 650.degree. C. to about 900.degree. C. may be used. It will be appreciated that the effectiveness of the calcination step is a primary function of temperature and time, the economic optimum being readily determined by anyone skilled in the art.
U.S. Pat. No. 3,842,163, A. S. Russell et al., entitled "Production of Aluminum Chloride" and assignors to Aluminum Company of America, state, to quote lines 45 to 58:
The U.S. Department of the Interior, Information Circular i4l2 by Robert L. de Beauchamp, sums up the problem of producing AlCl.sub.3 from various materials on page 6, the last paragraph reading as follows:
Canadian Pat. No. 569,830 to Groth in 1939 described a method for chlorinating aluminiferous materials by treating dehydrated and crushed raw materials with aluminum chloride vapor at 600.degree. C.-900.degree. C., removing hot reaction gases containing iron chloride and titanium chloride, treating the residue with chlorine and a reducing agent, and processing the recovered aluminum chloride vapor containing silicon chloride and carbon monoxide at temperatures above 800.degree. C. with alumina or aluminous materials free from iron and titanium. The gases recovered from the chlorination process are oxidized to convert at least the chlorides of iron and titanium to their oxides prior to condensation. Therefore, because of the oxidation step, chlorides of the materials are not recovered in reusable form. Further, the vapor mixture recovered cannot be diluted with CO in order that the oxidation stage can be carried out.
Groth, Column 1, lines 28 to 32:
Weston, U.S. Pat. No. 4,277,446, in the first chlorination stage, depends upon the use of excess aluminum chloride containing FeCl.sub.3 that is recovered from the circuit and returned to chlorinate the Fe.sub.2 O.sub.3. To quote, Column 8, lines 30-34:
Reynolds et al., U.S. Pat. No. 4,288,414, describe a process for the production of aluminum of substantially high purity from chlorination of clays associated with coal and bauxite. The improvements stated are forming the feed material into carbon-free briquettes, and introducing silicon chloride into the reductive chlorination step to further suppress the chlorination of siliceous materials contained in the feed. To differentially chlorinate the iron they describe using an oxidizing atmosphere wherein the iron is vaporized.
The first stage of column 2, lines 62 to 66 states:
Column 4, lines 1 to 4 states:
In my claimed invention, using a reducing atmosphere, in excess of 90% of the contained iron in the calcined agglomerated product was chlorinated with less than 2% cochlorination of the contained alumina.
Further, contrary to the teachings of Reynolds et al., an important stage in my invention is to form agglomerates of the material in a specific size range and with comparatively low density, preferably in the bulk density range of 0.8 to about 1.2 following subsequent calcination. Thus, in the claimed process, contrary to the art, high pressure pelletizing or briquetting are avoided.